DEVELOPMENTAL ANALYSIS AND SUBCELLULAR-LOCALIZATION OF THE MURINE HOMOLOG OF ELL

The ELL gene was first identified by its involvement with MLL in the t ranslocation (11;19)(q23;p13.1) in acute myeloid leukemia, To date, ni ne other MLL partner genes have been cloned, but their precise functio ns have get to be determined. To characterize the functions of ELL fur ther, we have cloned the murine homologue of ELL and have found that t he gene is highly conserved at the nucleotide and amino acid level, Th e open reading frame of the murine homologue contains 602 aa, slightly smaller than the 621 aa in the human gene, With Northern blot analysi s, a 3.4-kb transcript is detected in all tissues examined with greate st levels of expression in the liver, Unlike human ELL, only a single transcript can be detected with either murine coding sequence or 3' un translated region probes, To examine the spatial and temporal pattern of expression in murine development, in situ hybridization studies wer e performed with sense and antisense riboprobes from the 3' untranslat ed region of murine Ell. Ell is expressed diffusely by embryonic day 7 .5 (E7.5), In addition, high levels of expression can he detected in m aternally derived decidual tissue, At E14.5, Ell is expressed diffusel y throughout the embryo. However by E16.5, specific expression in the liver and gastrointestinal tract becomes prominent and remains so in b oth neonates and adults, To determine the subcellular localization of ELL, we developed a polyclonal antiserum to ELL that was used for immu nofluorescence studies in COS-7, HeLa, NIH 3T3, and A7r5 cells, The EL L protein was localized to the nucleus but excluded from nucleoli in a ll cell lines examined, Recently, the gene product of ELL was found to function as an RNA polymerase II elongation factor, an activity that is consistent with our immunofluorescence data, Thus, these studies ex tend our understanding of the normal functions of ELL and provide addi tional insight into its aberrant function when fused to MLL in acute m yeloid leukemia.